U.S. patent application number 14/426075 was filed with the patent office on 2015-08-06 for method and apparatus for rapid molding a composite structure.
The applicant listed for this patent is FIVES MACHINING SYSTEMS, INC.. Invention is credited to Daniel Allman, Richard A. Curless.
Application Number | 20150217488 14/426075 |
Document ID | / |
Family ID | 50237680 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150217488 |
Kind Code |
A1 |
Allman; Daniel ; et
al. |
August 6, 2015 |
METHOD AND APPARATUS FOR RAPID MOLDING A COMPOSITE STRUCTURE
Abstract
A method for molding a composite structure includes the steps of
infusing a fabric with a resin to form a ply of composite material,
transferring the ply of composite material to a preheat station,
and preheating the ply of composite material to a temperature that
renders the composite material more drapable, but is less than a
temperature that causes the resin in the material to initiate
polymerization. The ply of composite material is then transferred
to a press station where it is heated to a temperature that causes
the resin to initiate polymerization, whereby the curing time for
the composite material is substantially less than the curing time
of a fabric that is infused with an epoxy resin.
Inventors: |
Allman; Daniel; (Hebron,
KY) ; Curless; Richard A.; (Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FIVES MACHINING SYSTEMS, INC. |
Fond du Lac |
WI |
US |
|
|
Family ID: |
50237680 |
Appl. No.: |
14/426075 |
Filed: |
September 9, 2013 |
PCT Filed: |
September 9, 2013 |
PCT NO: |
PCT/US2013/058759 |
371 Date: |
March 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61698130 |
Sep 7, 2012 |
|
|
|
Current U.S.
Class: |
264/152 ;
264/258 |
Current CPC
Class: |
B29C 35/02 20130101;
B29C 70/56 20130101; B29C 2043/189 20130101; B29C 43/203 20130101;
B29C 70/48 20130101; B29L 2009/00 20130101; B29C 2035/0283
20130101; B29C 43/18 20130101; B29C 70/541 20130101; B29K 2063/00
20130101; B29K 2031/00 20130101 |
International
Class: |
B29C 43/18 20060101
B29C043/18; B29C 43/20 20060101 B29C043/20 |
Claims
1. A method for molding a composite structure into a part, the
method comprising the following sequence of steps: infusing a
fabric with a resin to form a ply of composite material comprising
a resin infused fabric; stacking a number of plies of composite
material to form a charge; placing the charge in a tension cassette
and engaging the charge with grippers to maintain the relative
alignment and orientation of the plies of the charge relative to
one another; placing the charge under tension in the tension
cassette; transferring the charge of composite material in the
tension cassette to a preheat station; preheating the of composite
material at the preheat station to a preheat temperature that
renders the composite material more drapable but is less than a
temperature that causes the resin in the material to initiate
polymerization and maintaining the tension on the charge in the
cassette while it is being preheated; transferring the charge of
composite material in the tension cassette to a press station; and
heating the charge of composite material at the press station to a
temperature that causes the resin to initiate polymerization,
whereby the curing time for the composite material is substantially
less than the curing time of a fabric that is infused with an epoxy
resin.
2. (canceled)
3. The method of claim 2 further comprising: maintaining the
tension on the charge of composite material when it is being heated
at the press station.
4. The method of claim 1 further comprising: using a form and cure
assembly at the press station that includes press platens to heat
the charge of composite material to a temperature that causes the
resin to initiate polymerization.
5. The method of claim 1 further comprising: varying the tension
across the charge of composite material depending on the final
shape of the part.
6. (canceled)
7. (canceled)
8. The method of claim 1 further comprising: exerting a tension on
the charge from at least the time when the charge is being
pre-heated in the preheat station to the time that the charge is
being heated in the press station.
9. (canceled)
10. The method of claim 1 further comprising: selecting the resin
from a group consisting of thermosetting and thermoplastic
resins.
11. The method of claim 10 wherein the resin is solid at room
temperature and can be stored for a period of at least 6
months.
12. The method of claim 10 wherein the resin is a thermosetting
resin.
13. The method of claim 12 wherein the thermosetting resin is a
vinyl ester.
14. The method of claim 10 wherein the resin is a thermoplastic
resin.
15. The method of claim 3 further comprising: varying the tension
exerted by the grippers on the charge depending on the final shape
of the part.
16. The method of claim 11 further comprising: making selective
relief cuts in the plies of composite material to enable the
material to be molded into a final shape without exerting excess
stress on the fibers in the plies.
17. The method of claim 1 further comprising: providing heating
elements at the preheat station; and individually controlling the
heating elements to create heating zones within the preheat station
in order to heat selected sections of the charge to control
drapability.
18. The method of claim 1 further comprising: preheating the
tensioned charge to a temperature of between 100.degree. F. and
500.degree. F. at the preheat station.
19. The method of claim 1 further comprising: preheating the
tensioned charge to a temperature of between 120.degree. F. and
190.degree. F. at the preheat station.
20. The method of claim 4 further comprising: heating the charge in
the form and cure assembly to a temperature of between 250.degree.
F. and 350.degree. F.
21. The method of claim 4 further comprising: heating the charge in
the form and cure assembly to a temperature of between 70.degree.
F. and 120.degree. F.
Description
FIELD
[0001] The device relates to a method and apparatus for rapid
molding composite parts in which part shapes are cut from a
pre-impregnated continuous fiber reinforced material to form a
charge, the charge is held in tension while it is preheated to a
certain temperature, and the preheated charge is placed in a
forming and curing tool where tension is applied to the charge
while the heated tool halves are closed and the part is rapidly
cured.
BACKGROUND
[0002] The cost effective production of parts for the automotive
industry is dependent on efficient repeatable manufacturing
processes that deliver quality parts at a high volume. In order to
meet cost and quality demands in the automotive market, it is
necessary to constantly re-invent manufacturing technologies.
Additionally the global automotive market is seeking
"light-weighting" materials and manufacturing technologies that
enable mass and weight reduction to improve fuel efficiencies. The
composites (fiber reinforced materials) industry has a long history
in supplying automotive parts primarily for lower volume vehicles
such as the Chevrolet Corvette and Dodge Viper. However,
traditional composite processes such as Sheet Molding Compound
(SMC) and Long Fiber Thermoplastic (LFT) utilize discontinuous
fibers that significantly reduce the strength and stiffness of the
materials. Processes such as Resin Transfer Molding (RTM) can
utilize a continuous (dry) fiber, but RTM processes have
historically failed to support the quality and manufacturing
efficiencies demanded by automotive OEM's. Long cycle times, high
labor content, and high scrap and rework costs are typical when
attempting rapid cycle RTM processes. Continuous fiber materials
offer the highest level of light-weighting capability available to
the automotive industry. Although utilized extensively by the
aerospace industry for their light-weighting benefits, continuous
fiber materials have realized few applications in the automotive
industry due to slow and labor intensive manufacturing processes.
To utilize continuous fiber technology beyond the automotive
industries niche market volumes, and meet the auto industry's part
quality and cycle efficiencies requirements, new manufacturing
methods and mechanisms are required. Continuous fiber
reinforcements such as glass, carbon or other reinforcements that
are pre-impregnated with a thermoset or in some cases a
thermoplastic polymer are known as prepreg. In order to achieve the
desired strength and stiffness, a number of prepreg plies are often
stacked together to form a "charge". The fibers are oriented in the
direction of the structural load the part will experience in use
and under crash conditions. Once the charge is assembled,
maintaining the proper alignment and orientation of the fibers
during handling and the subsequent multiple processing steps to
produce the final part requires a unique and innovative material
and manufacturing solution.
[0003] It would accordingly be desirable to provide a method and
apparatus for producing composite parts that would enable the plies
and fibers of a charge to be maintained in the proper orientation
and in alignment with one another prior to the charge being
delivered into a forming and curing tool.
[0004] It would also be desirable to utilize a method and apparatus
for producing composite parts that would enable the plies and
fibers of a charge to be maintained in the proper orientation after
the charge is placed into a forming and curing tool and the mold
halves are closed onto the charge.
[0005] It would further be desirable to utilize a method and
apparatus for producing thermoset composite parts that would
shorten the cycle time required to cure the resin in a part in a
forming and curing tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIGS. 1A and 1B are plan views of an automated facility for
manufacturing composite parts.
[0007] FIGS. 2A and 2B are side views of the automated facility of
FIGS. 1A and 1B.
[0008] FIG. 3 shows a ply of material cut from a continuous fabric
of composite material with the fibers running in a first
direction.
[0009] FIG. 4 shows a ply of material cut from a continuous fabric
of composite material with the fibers running in a second
direction.
[0010] FIG. 5 shows the steps of a process for manufacturing a
composite part using a thermoset resin.
[0011] FIG. 6 shows the steps of a process for manufacturing a
composite part using a thermoplastic resin.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] Fiber reinforcement(s) are impregnated with either a
thermoset or thermoplastic resin to form a prepreg material. The
prepreg may comprise reinforcing fiber such as glass, carbon, or
other fibers commonly used in composite structures, or a
combination thereof, as known to those skilled in the art. The
prepreg may also be reinforced with Basalt, natural or other
fibers. The resin may comprise a single resin that may be a
thermosetting resin of a vinyl ester. A thermosetting resin such as
a vinyl ester provides the following advantages: the resin is solid
at room temperature, the resin has a shelf life of ten months, and
the resin has a rapid cure time in the mold. A thermosetting, vinyl
ester resin that cures, or polymerizes, at approximately
300.degree. F. enables the rapid cycle efficiencies similar to a
thermoplastic polymerprocess. The prepreg material may be wound
onto a roll for storage at room temperature, and later handling in
a manufacturing process.
[0013] As shown in FIGS. 1A, 1B, 2A and 2B, an automated line for
the production of composite parts is generally designated by the
reference numeral 10. The prepreg material 12 may be delivered from
a roll 13 as a broadgood to a cutting station 15 where the prepreg
may be cut into net or near net shaped pieces that may be combined
to form finished parts. The cutting station 15 may be used to cut
the composite material 12 from the roll 13 into plies having shapes
that may be similar to the final shape of a part. The cutting
station 15 may cut several plies of the composite material 12 to
the same shape. As shown in FIGS. 3 and 4, the prepreg material 12
may be cut so that the fibers 16 in each cut piece 17 and 18 are
oriented in the desired direction in order to impart the required
strength characteristics to the finished part. The cutting station
15 may also be used to make selective relief cuts 19 in the plies
of composite material 12 to enable the material 12 to be molded
into a final shape without exerting excess stress on the fibers in
the plies. The width and thickness of the composite prepreg
material 12 may be determined by the overall "string" dimensions of
the part geometry being considered for production.
[0014] The cut pieces 17 and 18 may be transferred to a
pre-consolidation station 21 until the desired number of fabric
layers or plies are assembled. The plies may be consolidated to
form a charge 22, and individual charges 22 may be transferred to a
stacking station 25 for later processing. The pre-consolidation of
cut pieces 17 and 18 into charges 22 may be achieved by stacking
the individual plies on top of one another, since the tack
properties of the vinyl resin will enable the individual plies 17
and 18 to adhere to one another. The pre-consolidation may also be
achieved by applying a light pressure in the range of 1-300 PSI to
a stack of plies. The wide range of consolidation pressures is
driven by the nature of the specific polymer, formulation and fiber
volume fraction selected for the specific application and end use
requirements. For example, a low tack epoxy material will have a
higher consolidation pressure in the range of 200-300 PSI, and a
high tack vinyl ester will have a lower consolidation pressure in
the range of 1-50 PSI. Additionally a high fiber loaded composite
will have a higher consolidation pressure in the range of 150-200
PSI, while a low fiber loaded material will have a lower
consolidation pressure in the range of 100-150 PSI. Transfer of the
cut pieces from the cutting station 15 to the pre-consolidation
station 21, and from the pre-consolidation station to the stacking
station 25, and to other stations downstream from the stacking
station, may be performed by a robot 27 which may be mounted on
rails 28, or other material handling device, or the transfer may be
performed manually, without departing from the spirit of the
present disclosure.
[0015] Individual charges 22 from the stacking station 25 may be
taken to a loading station 29 where they are loaded into a cassette
31. The cassette 31 surrounds the charge 22 and allows secure
automated handling and positioning of the charge through subsequent
steps of the process. The cassette 31 may have sets of discrete
grippers 32 that engage the charge 22 on two opposite ends, or
around the entire periphery of the charge 22, and pull on the
charge to place the charge in tension. The grippers 32 may be used
to hold the plies and fibers 16 of a charge 22 in the proper
orientation and in alignment with one another prior to the charge
being placed into a forming and curing tool downstream from the
loading station 29. The tension may be from 0.1 lb to 10 lbs, and
more particularly from 3-10 lbs. In one embodiment, the tension of
2 lbs was employed. The tension exerted by the grippers 32 may vary
across the surface of the charge 22 depending on the final shape of
the part.
[0016] The charge 22 in the tension cassette 31 may then be
transferred to a preheating station 30 where it is pre-heated in a
preheating oven 35 to a preheat temperature between 100.degree. to
500.degree. F. while it is being held in tension by the grippers
32. The wide process temperature range is determined by the polymer
selected and the temperature range at which the polymer experiences
a phase change thus enabling high drapability or formability of the
next step of the process. For example, a polymer can be formulated
to soften at a temperature of 140.degree. F. or the same polymer
can be formulated to soften at 200.degree. F. The performance
specifications for the formed part will determine the specific
formulation. Typically a high glass transition temperature material
will have a higher process temperature than the same polymer with a
lower glass transition temperature due to the cross link density of
the system. The pre-heating oven 35 may use quartz or radiant
heating elements 37 that may be individually controlled to create
heating zones within the oven 35 in order to heat selected sections
of the charge to control drapability.
[0017] Pre-heating the prepreg while the material is held in the
tension cassette 31 increases the formability and drapability of
the charge 22 so that the composite material will more readily
conform to the final shape of the molded part in the downstream
form and cure tool 41 without disturbing the orientation and
placement of the fibers 16 in the individual layers or plies 17 and
18. Pre-heating the charge 22 prior to molding will also change the
thermosetting resin from a solid to a liquid state, thus minimizing
the influence of the resin's viscosity on the drapability of the
layered composite material during the molding process. In one
embodiment, the pre-heating oven 35 may be used to increase the
temperature of the thermoset prepreg charge to a preheat
temperature of 150.degree. F. The pre-heating also reduces the cure
time of the end product in the form and cure tool 41 since the time
required to increase the temperature of the charge 22 to initiate
the polymerization phase will be less than if the material was
introduced into the form and cure tool 41 at ambient temperature.
The preheat temperature is not high enough to initiate the free
radical initiation/polymerization phase of the polymer in the vinyl
ester resin. After pre-heating, the grippers 32 in the cassette 31
may continue to hold the charge 22 in tension while the charge is
transferred to the form and cure tool 41. An indexing conveyor 34
may be used to transfer the cassette 31 with the charge 22 from the
loading station 29 to the preheat station 30 and from the preheat
station 30 to a press station 40.
[0018] The pre-heated charge 22 may then be transferred from the
preheat station 30 to the press station 40 where it may be placed
into a heated form and cure tool 41. The form and cure tool 41 may
comprise a press 44 with opposed platens 42 and matched metal dies
43. For a thermoset polymer the temperature of the metal dies 43
may be set or ramped up to 350.degree. F., and more particularly
225-300.degree. F. to initiate the polymerization phase of the
resin in the charge 22. Once the charge 22 is placed in the form
and cure tool 41 and the metal dies 43 close on the charge 22, the
tension grippers 32 may release the charge 22 so that it can be
molded by the metal dies 43 into its final shape. The cassette 31
and the tension grippers 32 may then be returned to the stacking
station 25 to pick up the next charge. Pressure on the charge 22 in
the form and cure tool 41 is adjustable from 10 PSI to 1000 PSI,
and more particularly from 100-300 PSI. The forming pressure will
vary based on the polymer selected and the fiber volume fraction.
The average forming and curing cycle time of a charge 22 in the
form and cure tool 41 may be between 30 and 300 seconds, and in one
embodiment, the time of the charge 22 in the form and cure tool 41
was 60 seconds. The cure time of the polymer is influenced by the
polymer, the polymer formulation and the form and process tooling
temperature. In comparison, a charge of composite material
comprising an epoxy thermosetting resin of the same size and weight
typically requires a cycle time of at least 10 minutes.
[0019] The tension grippers 32 in the cassette 31 minimize
wrinkling of the composite material during the form and cure cycle
and maintain the desired orientation of the fibers 16 in each ply
during the formation of complex three dimensional parts. Instead of
being part of a separate cassette 31 as shown, the tension grippers
32 may be integrated into the form and cure tool 41. The
manufacturing process can be used, for example, to form relatively
large, high volume automobile parts, such as floor pans, roofs,
hoods, deck lids, and lift gates.
[0020] FIG. 5 shows the steps of the process 50 for manufacturing a
composite part using the apparatus as described above. In step 51,
glass or carbon fiber reinforcement may be infused with a
thermosetting resin of a vinyl ester to create a prepreg. In step
52, the prepreg material may be cut into net or near net shape
pieces. In step 53, the cut prepreg pieces may be stacked and
pre-consolidated to form a charge. In step 54, the charges may be
stacked at a stacking station. In step 55, the charges may be
loaded at a loading station into grippers on a cassette, and the
grippers may be used to exert a tension on the charge. In step 56,
the loaded cassette may be transferred into a pre-heat oven. In
step 57, the tensioned charge may be preheated in the pre-heat
oven. For a thermoset polymer, the preheat temperature is high
enough to increase the drapability of the charge, but low enough so
that polymerization is not initiated. In step 58, the preheated
charge in the tension cassette may be transferred into a form and
cure tool that is set or ramped up to 250-350.degree. F. In step
59, the forming and cure tool may be closed, and the tension
cassette releases the charge and returns to the loading station to
engage a new charge. In step 60, the forming and curing tool may be
used to heat the thermoset charge to between 250.degree. F. and
350.degree. F. under 10-1000 PSI, and more particularly under
100-300 PSI to form and cure the part. In step 61, the cured part
may be removed from the forming and curing tool. The forming and
curing cycle time may be as little as sixty seconds. The rapid
cycle time in the forming and curing tool in step 60 is enabled by
a combination of the use of the vinyl ester resin in step 51 and
preheating the charge in step 57 to the preheat temperature prior
to placing it in the forming and curing tool. The cycle time for
prior art processes for forming a similar part using an epoxy type
prepreg polymer is ten minutes or more.
[0021] The process described above may also be applied to prepreg
that is infused with thermoplastic resin according to the process
70 as shown in FIG. 6. In step 71, glass or carbon fiber
reinforcement may be infused with a thermoplastic resin to create a
prepreg. In step 72, the prepreg material may be cut into net or
near net shape pieces. In step 73, the cut prepreg pieces may be
stacked and pre-consolidated using heat to form a charge. In step
74, the charges may be stacked at a stacking station. In step 75, a
charge may be loaded at a loading station into grippers on a
cassette, and the grippers may be used to exert a tension on the
charge. In step 76, the loaded cassette may be transferred into a
pre-heat oven. In step 77, the tensioned charge may be preheated in
the pre-heat oven. For a thermoplastic prepreg material the preheat
temperature is typically within the melt profile of the polymer
that is being used. In step 78, the preheated charge in the tension
cassette may be transferred into a form and cure tool that is set
to 70.degree. F-120.degree. F. In step 79, the form and cure tool
may be closed, and the tension cassette may be returned to the
loading station to engage a new charge. In step 80, the form and
cure tool may be brought to a temperature of 70.degree.
F-120.degree. F. to form and cure the part. In step 81, the cured
part may be removed from the form and cure tool. As in the process
using a thermoset resin, when using the thermoplastic resin, the
tension grippers minimize wrinkling of the composite material
during the form and cure cycle and maintain the desired orientation
of the fibers in each ply during the formation of complex three
dimensional parts.
[0022] Having thus described the device, various modification and
alterations will occur to those skilled in the art, which
modification and alterations will be within the scope of the
invention as defined by the appended claims.
* * * * *